1. Field of the Invention
This invention relates generally to fluid valves and particularly to those capable of providing fluid direction control and switching functions at a substantially continuous rate.
2. Description of the Related Art
In order to enhance performance of their pumping systems, many manufacturers have replaced single acting pumps with double acting pumps. These reciprocating pumps typically utilize one or more cylinders together with appropriate valves for controlling fluid flow to and from the cylinders. The pumps are configured to simultaneously pump fluid from one cylinder while drawing fluid into another cylinder. When the fluid of the pumping cylinder is expended, the pump switches the pumping action to the other cylinder, while supplying the expended cylinder with fluid. This reciprocating action permits the pump to have a relatively continuous flow.
The double acting pumps may be connected to a rotating crossover valve that switches the fluid flow by rotating a cylindrical fluid director to communicate with various ports on the pump. These crossover valves, however, are required to operate under low to medium pressure in most applications but also very high pressures in many applications. For example, some applications may require pressures in excess of 3,000 psi. Additionally, many of the fluids that are being pumped in such applications contain coarse particles, which can cause significant wear and tear on the valve leading to valve leakage and failure.
The rotating crossover valves have several problems when operating under such conditions. For example, one problem is that the coarse particles are often drawn into an area between the rotating fluid director and stationary valve housing and wear the fluid director and housing. As a result, the rotatable crossover valves are unable to operate for long periods of time and frequently require replacement, typically of the entire crossover valve.